The present invention relates to an apparatus and method for producing marks, such as reference marks, on substrates.
Reference marks are applied on semiconductor substrates to allow precise positioning of the substrate in fabrication and inspection processes. In one inspection method, a light scattering surface inspection system is used to locate contaminant particles on the surface of the wafer. The contaminant particles are then assigned coordinates based on a reference grid which is established using the reference marks on the wafer. The wafer is then placed in a scanning electron microscope ("SEM"), and the reference marks on the wafer used to locate the coordinates of the contaminant particles on the wafer.
In such inspection processes, the reference marks on the wafer must be small. Small marks allow faster location of the coordinates for the contaminant particles in the SEM. Without fine marks, it takes an inordinate amount of time to locate the contaminant particles on the wafer. To be effective, the reference marks should be sized smaller than about 100 microns, and preferably sized from about 1 micron to about 60 microns.
It is difficult to create such fine reference marks. Mechanical scratching processes that use a sharp needle to scratch the surface of the wafer cause unacceptably large marks, which can increase the possibility of cracking the thin wafers. Typical laser etching processes have coarse optic systems that produce marks having sizes greater than about 100 microns, and laser etching processes with fine optic systems are expensive.
Further, current wafer marking processes often damage the region of the wafer surrounding the mark. For example, laser etching can "burn" the region surrounding the mark. Existing processes can also create contaminants that subsequently deposit on the regions of the wafer that surround the reference mark. These contaminants substantially decrease the yield of integrated circuit chips formed from the semiconductor wafer.
Thus, it is desirable to have a marking apparatus and process that can produce fine reference marks on substrates, without cracking the substrate, without damaging the surrounding regions, and without depositing contaminant particles on the substrate.